The present invention relates to poly[alkylene-4,4'-(ethylenedioxy)bis benzoate] copolymers as well as surgical devices formed therefrom. More particularly, this invention relates to flexible monofilament surgical sutures having unique handling and knot-tying characteristics.
Many natural and synthetic materials are presently used as surgical sutures. These materials may be used as single filament strands, i.e. monofilament sutures, or as multifilament strands in a braided, twisted or other multifilament construction. Natural materials such as silk, cotton, linen, and the like, do not lend themselves to the fabrication of monofilament sutures and are accordingly used mostly in one of the multifilament constructions.
Certain synthetic materials which are extruded in continuous lengths can be used in monofilament form. Common synthetic monofilament sutures include polypropylene, polyethylene and nylon 6. Such monofilament sutures are preferred by surgeons for many surgical applications due to their inherent smoothness and noncapillarity to body fluids.
Available synthetic monofilament sutures all suffer to a greater or lesser degree from one particular disadvantage, that is relative stiffness. Besides making the material more difficult to handle and use, suture stiffness or low compliance can adversely affect knot-tying ability and knot security. It is because of the inherent stiffness of available monofilament sutures that many suture materials are braided or have other multifilament constructions with better handling, flexibility and conformity.
Most monofilament sutures of the prior art are also characterized by a high degree of stiffness. This makes knot-tying difficult and reduces knot security. In addition, the low compliance and limited ductility prevent the suture from "giving" as a newly sutured wound swells, with the result that the suture may place the wound tissue under greater tension than is desirable, and may even cause some tearing, cutting or necrosis of the tissue.
The problems associated with the use of low compliance sutures in certain applications were recognized in U.S. Pat. No. 3,454,011, where it was proposed to fabricate a surgical suture composed of Spandex polyurethane. Such sutures, however, were too elastic and did not find general acceptance in the medical profession.
Recently issued U.S. Pat. No. 4,224,946 describes a monofilament suture with good flexibility and knot strength, which suture is composed of segmented polyetheresters which contain (1) a polymeric block of polyalkylene ethers and (2) a polymeric block of aromatic dicarboxylic acids or cycloaliphatic acids with short chain aliphatic or cycloaliphatic diols. Similar subject matter is disclosed in Belgian Pat. No. 880,486.
The ethylene glycol polyester of the subject diacid moiety, 4,4'-(ethylenedioxy)bis benzoic acid, has been known for some time, (C.A. Registry No. [24980-45-8] if prepared from the acid, [26373-72-8] if prepared from the dimethyl ester) and, in fact, its ethylene glycol/polytetramethylene oxide copolymers (C.A. Registry Nos. [9071-04-9] and [51884-53-8] have been prepared:
CA 76 114610y PA0 CA 80 83814u mentioned in index only PA0 CA 81 171028s PA0 CA 81 P12175g PA0 CA 83 P195002w manufacture of elastic fiber PA0 CA 84 P75556d polyester composite fibers with rubber-like elasticity) PA0 Knot strength--at least 20,000 psi PA0 Tensile strength--at least 30,000 psi PA0 Young's modulus--less than about 600,000 psi PA0 Elongation--from about 20% to 80% PA0 Knot strength--30,000 to 65,000 psi PA0 Tensile strength--45,000 to 100,000 psi (more preferably 60,000 to 100,000 psi) PA0 Young's modulus--75,000 to 600,000 psi (more preferably 75,000 to 250,000 psi) PA0 Elongation--from 20% to 55%
as well as copolymers based on polyethylene oxide. These polyesters have been described as possessing improved crimpability, dyeability, and moisture absorption properties.
The 1,4-butanediol polyester of the subject diacid moiety is disclosed in Chemical Abstracts [52826-06-9]. In a 1978 paper (C.A. 89 60077c) which relates to the transesterification of dimethyl esters of aromatic dicarboxy acids with .alpha.-hydro-.omega.-hydroxy poly(oxyethylene)s and .alpha.,.omega.-alkanediols, a polytetramethylene oxide/1,4-butanediol copolymer based on the subject diacid moiety was made.
In spite of the fact that several polyethers could be incorporated chemically to toughen and lower the modulus of related polyesters, it is generally accepted that linear thermoplastics possessing a high initial modulus are more difficult to modify to increase compliance. Fibers of the (all hard) homopolymers of the subject invention were found to possess moduli in excess of 1.5 million psi, which renders it unsuitable for producing monofilament sutures. Patents that relate to (2-alkenyl or alkyl)succinates are U.S. Pat. No. 3,542,737 and U.S. Pat. No. 3,890,279. None of these patents discloses the present copolymers or modifications thereof.
Theory and experience in the art of fiber chemistry predict that branching (such as that present in the instant copolymers) may inhibit fiber formation and will exert a deleterious effect on the tensile properties of any resulting fibers due to the inability of the unoriented branch to contribute to the load bearing capacity of the fiber; and by the stearic interference posed by the branch to chain alignment during fiber orientation. It is therefore surprising that strong fibers, in particular strong, flexible compliant fibers may be formed from the present copolymers with pendant hydrocarbon chains. As will be seen from Table 1, Example (i), homopolymers prepared from the 1,4-butanediol polyester of the subject diacid moiety, have a modulus of 1,678,000 psi. It is surprising that the modulus of certain of the copolymers of the present invention is reduced to only 64,000 psi.
It is an object of the present invention to provide a novel copolymer of poly(alkylene-4,4'-(ethylenedioxy)bis benzoate) as well as surgical devices formed therefrom. It is a further object of the present invention to provide a novel flexible, thermoplastic monofilament suture or ligature of said copolymer, having a diameter of from about 0.1 to 50 mil and possessing unique and desirable physical properties. Yet a further object of the present invention is to provide a Cobalt 60 sterilizable monofilament with lower modulus, better hand and more desirable tie-down characteristics than those of monofilaments of polypropylene. It is a further object of this invention to provide a monofilament suture with a desirable degree of ductility to accommodate changing wound conditions. It is yet another object of this invention to provide a monofilament suture with the flexibility and knot-tying characteristics of a braided suture. These and other objects will be made apparent from the ensuing description and claims.